1. Field of the Invention
The present invention generally relates to pump monitoring systems and, more specifically, to methods and systems for monitoring and evaluating fluidborne noise levels in a fluid circuit.
2. Description of Related Art
Steering noise is one of the deep-rooted concerns affecting vehicle marketability. Fluidborne noise is one major type of noise that can be heard in a hydraulic power steering system. In the system, the power steering pump is the fluidborne noise source that delivers fluctuating flows i.e., flow ripples, to the system. The flow ripple and the source impedance of the pump then interact with the connected hose, tubing, and steering gearbox to generate pressure pulsations.
The pressure pulsations are transmitted through the fluid to everywhere in the system and may excite dangerous mechanical vibrations and high levels of airborne noise. Currently, the conventional method to judge the source fluidborne noise characteristics of power steering pumps is to measure actual pressure pulsation levels at one location in a given pump-hose-valve bench system, which is known in the art as the xe2x80x9cone pressurexe2x80x9d method.
However, there are several technical problems with the current method. First, the results obtained from the current method are significantly dependent on the entire measurement system. That is, slight changes to the dimensions of connection pipes and/or the characteristics of the loading valve will result in totally different results. This makes it difficult or impossible to compare test results obtained in different geographical places. Second, the results obtained may not reflect actual noise levels or trends when the pump is installed in an actual power steering system because the impedance characteristics of the bench loading valve are different from those of the power steering gearbox. Finally, the results are the combined effect of the entire measurement system and they cannot be used as objective scaling for the inherent fluidborne noise properties of the pump.
The present invention is directed toward a method and system for determining the source fluidborne noise characteristics of a power steering pump. In accordance with the system of the present invention, the pump discharge is connected to a reference pipe that has three pressure sensors disposed therein at predetermined spacings from one another and from the pump discharge. First and second loading valves are disposed downstream the reference pipe and are fluidly connected by an extension pipe. Pump rotational speed is monitored by a photoelectric detector.
In further accordance with the present invention, the system includes a calculating and analysis assembly including an amplifying and filtering device, a fast Fourier transform (FFT) analyzer, and a computer. The calculating and analysis assembly uses pressure signals from the pressure sensors, together with known fluid dynamic properties of the reference pipe, the unknown properties of the fluid, and the known spacing between the sensors to calculate the source flow ripple and the internal impedance of the pump. The source flow ripple and internal impedance are subsequently used to determine the source flow ripple level, which is indicative of the noise characteristics of the pump.